EV battery pack cooling system

ABSTRACT

A battery pack thermal management assembly is provided for use with an electric vehicle in which the battery pack is sealed and mounted under the car. The batteries contained within the battery pack are thermally coupled via a layer of thermally conductive material to the interior surface of the pack&#39;s upper enclosure panel. The upper enclosure panel is thermally coupled via an interposed panel to a conduit structure, the conduit structure formed by a shaped conduit panel that is attached to a secondary panel.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/040,259, filed 10 Jan. 2016, which is a continuation-in-partof U.S. patent application Ser. No. 15/040,204, filed 10 Jan. 2016, thedisclosures of which are incorporated herein by reference for any andall purposes.

FIELD OF THE INVENTION

The present invention relates generally to battery packs and, moreparticularly, to a system for maintaining battery pack temperature whileminimizing the risks to passengers in the event of one or more of thebatteries within the battery pack entering into thermal runaway.

BACKGROUND OF THE INVENTION

In response to the demands of consumers who are driven both byever-escalating fuel prices and the dire consequences of global warming,the automobile industry is slowly starting to embrace the need forultra-low emission, high efficiency cars. While some within the industryare attempting to achieve these goals by engineering more efficientinternal combustion engines, others are incorporating hybrid orall-electric drive trains into their vehicle line-ups. To meet consumerexpectations, however, the automobile industry must not only achieve agreener drive train, but must do so while maintaining reasonable levelsof performance, range, reliability, safety and cost.

In recent years there have been several incidents of a rechargeablebattery pack, contained within a laptop computer or utilized in avehicle, catching on fire. As a result, one of the primary issuesimpacting consumer confidence with respect to both hybrid andall-electric vehicles is the risk of a battery pack fire.

Rechargeable batteries, due to their chemistries, tend to be relativelyunstable and prone to thermal runaway, an event that occurs when abattery's internal reaction rate increases to such an extent that it isgenerating more heat than can be withdrawn. If reaction rate and heatgeneration go unabated, eventually the heat generated becomes greatenough to cause the battery and materials in proximity to the battery tocombust. Thermal runaway may be the result of a battery short, forexample a short due to a leak within an internal battery pack coolingsystem. Thermal runaway may also be caused by a manufacturing defect,improper cell use, exposure to extreme temperatures, or damage such asthat which may be sustained during an accident or when road debris dentsor punctures the battery pack.

Although the prior art discloses numerous techniques for cooling thebattery pack of an electric vehicle, a thermal management system isneeded that is both cost effective and capable of maintaining thebatteries within their desired operating temperature range whileminimizing the risks to the vehicle's passengers. The present inventionprovides such a system.

SUMMARY OF THE INVENTION

The present invention provides a battery pack thermal managementassembly comprising (i) a plurality of batteries, where a first endportion of each battery includes both a first terminal and a secondterminal; (ii) a sealed battery pack enclosure configured to contain theplurality of batteries, the sealed battery pack enclosure comprising alower enclosure panel, a plurality of enclosure side panels, and anupper enclosure panel, and where the upper enclosure panel is comprisedof a thermally conductive material; (iii) a conduit panel, where atleast a portion of the conduit panel in cross-section exhibits acorrugated structure, where the corrugated structure is comprised of aplurality of mounting surfaces and a plurality of channels; (iv) asecondary panel, where a first surface of the secondary panel isattached to the conduit panel at a plurality of attachment junctures,where at least a portion of the plurality of attachment junctures areformed between the first surface of the secondary panel and theplurality of mounting surfaces, where the plurality of attachmentjunctures form a coolant channel seal, where the conduit panel and thesecondary panel form a cooling panel structure, where the cooling panelstructure comprises a coolant channel, and where the coolant channel isdefined by the first surface of said secondary panel and an innersurface of the plurality of channels of the corrugated structure of theconduit panel; (v) a tertiary panel interposed between an externalsurface of the upper enclosure panel and a second surface of thesecondary panel, where the tertiary panel is thermally coupled to theupper enclosure panel and the secondary panel; and (vi) a layer ofthermally conductive material, where the layer of thermally conductivematerial is electrically insulative, where the layer of thermallyconductive material contacts and is thermally coupled to at least anupper surface of each battery of the plurality of batteries, where theupper surface of each battery is distal from the first end portion ofeach battery, and where the layer of thermally conductive material isinterposed between the upper surface of each battery of the plurality ofbatteries and an internal surface of the upper enclosure panel. Theassembly may further include a heat transfer medium contained within thecoolant channel and a circulation pump configured to pump the heattransfer medium through the coolant channel.

In one aspect, the cooling panel structure may be attached to thetertiary panel using a temporary means of attachment such as bolts orclips. Alternately, the cooling panel structure may be attached to thetertiary panel using a technique selected from welding, brazing,soldering and bonding.

In another aspect, the tertiary panel may be attached to the upperenclosure panel using a temporary means of attachment such as bolts orclips. Alternately, the tertiary panel may be attached to the upperenclosure panel using a technique selected from welding, brazing,soldering and bonding.

In another aspect, the assembly may further include a layer of a thermalcompound interposed between a first surface of the tertiary panel andthe second surface of the secondary panel, where the thermal compoundmay be selected from the group consisting of thermal greases, thermalpastes and thermal gels.

In another aspect, the assembly may further include a layer of a thermalcompound interposed between the external surface of the upper enclosurepanel and the tertiary panel, where the thermal compound may be selectedfrom the group consisting of thermal greases, thermal pastes and thermalgels.

In another aspect, the sealed battery pack may be mounted to a vehicleand positioned such that the first end portion of each battery is inclose proximity to the lower enclosure panel, which in turn is adjacentto the road surface, and where the upper surface of each battery is inclose proximity to the internal surface of the upper enclosure panel.Preferably the batteries utilize a cylindrical form factor (e.g., 18650form factor) and are positioned within the battery pack such that thecylindrical axis corresponding to each battery is substantiallyperpendicular to the lower enclosure panel. In this configuration thecoolant channel is positioned such that the coolant within the coolantchannel will flow within a plane that is substantially perpendicular tothe cylindrical axis of each battery.

In another aspect, the plurality of attachment junctures may befabricated using a technique such as welding, brazing, soldering orbonding, thus creating a juncture comprised of a weld joint, brazejoint, solder joint or bond joint.

In another aspect, the layer of thermally conductive material may bediscontinuous and comprised of a plurality of thermally conductivematerial regions corresponding to the plurality of batteries.

In another aspect, the layer of thermally conductive material may beconfigured to contact and be thermally coupled to a second end portionof each battery of the plurality of batteries, where the second endportion of each battery is distal from the first end portion of eachbattery.

In another aspect, the layer of thermally conductive material preferablyhas a resistivity of at least 10¹² ohm-cm and a thermal conductivity ofat least 0.25 Wm⁻¹K⁻¹, and more preferably a resistivity of at least10¹² ohm-cm and a thermal conductivity of at least 0.75 Wm⁻¹K⁻¹. Thelayer of thermally conductive material may be comprised of an epoxy.

In another aspect, a plurality of granules may be dispersed throughoutthe layer of thermally conductive material, where the granules have amelting point that is higher than the melting point of the layer ofthermally conductive material.

In another aspect, the upper enclosure panel, which is preferably flat,may be fabricated from a metal such as aluminum or an iron alloy (e.g.,carbon steel, stainless steel, etc.). Preferably the upper enclosurepanel has a thermal conductivity of at least 15 Wm⁻¹K⁻¹, more preferablyat least 40 Wm⁻¹K⁻¹, and still more preferably at least 100 Wm⁻¹K⁻¹.

In another aspect, the secondary panel, which is preferably flat, may befabricated from a metal such as aluminum or an iron alloy (e.g., carbonsteel, stainless steel, etc.). Preferably the secondary panel has athermal conductivity of at least 15 Wm⁻¹K⁻¹, more preferably at least 40Wm⁻¹K⁻¹, and still more preferably at least 100 Wm⁻¹K⁻¹.

In another aspect, the tertiary panel, which is preferably flat, may befabricated from a metal such as aluminum or an iron alloy (e.g., carbonsteel, stainless steel, etc.). Preferably the tertiary panel has athermal conductivity of at least 15 Wm⁻¹K⁻¹, more preferably at least 40Wm⁻¹K⁻¹, and still more preferably at least 100 Wm⁻¹K⁻¹.

In another aspect, the conduit panel may be fabricated from a metal suchas aluminum or an iron alloy (e.g., carbon steel, stainless steel,etc.).

In another aspect, the inner surface of the upper enclosure panel may becoated with an isolation layer comprised of an electricallynon-conductive material. For example, if the upper enclosure panel isfabricated from aluminum the inner surface may be anodized.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

It should be understood that the accompanying figures are only meant toillustrate, not limit, the scope of the invention and should not beconsidered to be to scale. Additionally, the same reference label ondifferent figures should be understood to refer to the same component ora component of similar functionality.

FIG. 1 provides a perspective view of a battery pack and the vehiclechassis to which it is to be mounted;

FIG. 2 provides a cross-sectional view of a portion of an exemplarybattery pack in accordance with the prior art;

FIG. 3 provides a cross-sectional view of a portion of an alternatebattery pack configuration in accordance with the prior art;

FIG. 4 illustrates an exemplary battery pack cooling system inaccordance with the prior art;

FIG. 5 illustrates an alternate battery pack cooling system inaccordance with the prior art;

FIG. 6 illustrates an alternate battery pack cooling system inaccordance with the prior art, the illustrated system utilizing both aradiator and a heat exchanger as described relative to FIGS. 4 and 5,respectively;

FIG. 7 illustrates the exemplary cooling system shown in FIG. 4 with adifferent coolant conduit configuration within the battery pack;

FIG. 8 provides a cross-sectional view of a preferred embodiment of theinvention;

FIG. 9 provides a schematic diagram of a simplified battery packconfiguration in which the bus bars are only adjacent to one end of thebatteries;

FIG. 10 provides a cross-sectional view of the embodiment shown in FIG.8, modified to include a continuous layer of thermally conductivematerial within the battery pack;

FIG. 11 is a top view of battery pack shown in FIG. 8, this view showingthe pattern of coolant conduits formed in the top panel;

FIG. 12 provides a cross-sectional view of the embodiment shown in FIG.8 utilizing a conduit panel with a different cross-section and channelpitch;

FIG. 13 provides a cross-sectional view of the embodiment shown in FIG.8, this view illustrating the effects of a small leak between thebattery pack enclosure panel and the conduit panel;

FIG. 14 provides a cross-sectional view of an embodiment similar to thatshown in FIG. 8 except for the inclusion of an additional layer betweenthe upper battery pack enclosure panel and the conduit panel; and

FIG. 15 provides a cross-sectional view of an embodiment similar to thatshown in FIG. 8 except for the inclusion of two additional layersbetween the upper battery pack enclosure panel and the conduit panel.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises”, “comprising”, “includes”, and/or“including”, as used herein, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features, processsteps, operations, elements, components, and/or groups thereof. As usedherein, the term “and/or” and the symbol “/” are meant to include anyand all combinations of one or more of the associated listed items.Additionally, while the terms first, second, etc. may be used herein todescribe various steps, calculations or components, these steps,calculations or components should not be limited by these terms, ratherthese terms are only used to distinguish one step, calculation orcomponent from another. For example, a first calculation could be termeda second calculation, and, similarly, a first step could be termed asecond step, without departing from the scope of this disclosure.

In the following text, the terms “battery”, “cell”, and “battery cell”may be used interchangeably and may refer to any of a variety ofdifferent battery configurations and chemistries. Typical batterychemistries include, but are not limited to, lithium ion, lithium ionpolymer, nickel metal hydride, nickel cadmium, nickel hydrogen, nickelzinc, and silver zinc. The term “battery pack” as used herein refers toan assembly of batteries electrically interconnected to achieve thedesired voltage and capacity, where the battery assembly is typicallycontained within an enclosure. The terms “electric vehicle” and “EV” maybe used interchangeably and may refer to an all-electric vehicle, aplug-in hybrid vehicle, also referred to as a PHEV, or a hybrid vehicle,also referred to as a HEV, where a hybrid vehicle utilizes multiplesources of propulsion including an electric drive system.

In a conventional EV with a large battery pack, such as that typicallyrequired for an all-electric vehicle or a PHEV with a relatively longelectric-only range, the battery pack is normally mounted under thevehicle, and thus at least partially under the vehicle's passengercabin. This mounting location is generally considered to be optimal,both from a packaging point of view in terms of minimizing the impact onthe passenger and luggage compartments as well as from a vehicleperformance point of view in terms of providing a low center of gravityand a desirable weight distribution. The typical undercarriageconfiguration described above is illustrated in FIG. 1 which shows abattery pack 101 configured to be mounted from below, followingdirection 103, into vehicle chassis 105. Once mounted, battery pack 101traverses the width of the vehicle and extends substantially between thefront and rear suspension assemblies.

FIGS. 2 and 3 provide cross-sectional views of exemplary batteryconfigurations suitable for use in a battery pack such as that shown inFIG. 1. For purposes of clarity, battery interconnects and batterymounts are not included in either of these figures. Visible in FIGS. 2and 3 is a portion of the upper battery pack enclosure panel 201, aportion of the lower battery pack enclosure panel 203, and a pluralityof batteries 205. Note that the enclosure side panels are not visible inthis view. Batteries 205 shown in these exemplary configurations utilizean 18650 form-factor and are positioned such that the axis of eachbattery, i.e. the cylindrical axis, is substantially perpendicular toboth lower enclosure panel 203 and surface 207 of the road. In batterypack configuration 200, interposed between the base of each cylindricalbattery 205 and lower panel 203 are a plurality of cooling conduits 209through which a liquid coolant, i.e., a heat transfer medium, is pumped.Alternately, and as illustrated in battery pack configuration 300,cooling conduits 301 are interposed between the sides of adjacentbatteries 205. In both of the illustrated configurations, the coolingconduits are aligned with lower panel 203, resulting in the coolantwithin channels 211/303 flowing in a direction substantiallyperpendicular to the axes of the cylindrical batteries. By regulatingthe flow of coolant within conduits 209/301 and/or regulating thetransfer of heat from the coolant to another temperature control system,the temperature of cells 205 may be regulated so that the cells remainwithin their preferred operating range. In the illustratedconfigurations, one or more thermally insulating layers 213 areinterposed between the batteries/cooling conduits and the battery pack,thereby providing a means for limiting the unintentional transfer ofthermal energy between the batteries/cooling conduits and the batterypack enclosure. Thermally insulating layer(s) 213 may be comprised ofair or some other thermally insulating material.

FIG. 4 illustrates an exemplary battery thermal management system 400suitable for use with a battery pack such as that described herein. Insystem 400, the temperature of the batteries within battery pack 101 iscontrolled by pumping a thermal transfer medium, e.g., a liquid coolant,through a plurality of battery cooling conduits 401. Cooling conduitsmay be integrated into battery pack 101 as described above relative toFIGS. 2 and 3, or coupled to an exterior surface of battery pack 101 asdescribed below relative to the present invention. Conduits 401, whichare in thermal communication with the batteries within pack 101, providea means of controlling the temperature of the batteries by regulatingthe flow of coolant within conduits 401 and/or regulating the transferof heat from the coolant to another temperature control system. In theembodiment illustrated in FIG. 4, the coolant within conduits 401 ispumped through a radiator 403 using a pump 405. A blower fan 407 may beused to force air through radiator 403, for example when the car isstationary or moving at low speeds, thus insuring that there is anadequate transfer of thermal energy from the coolant to the ambientenvironment. System 400 may also include a heater 409, e.g., a PTCheater, that may be used to heat the coolant within conduits 401, andthus heat the batteries within pack 101. Battery heating via asupplemental heat source 409 or by coupling the battery pack coolantloop to various drive train components (e.g., motor, power inverter,transmission, etc.) may be necessary to maintain battery temperaturewithin the desired operating range, for example when the ambienttemperature is too low or during initial vehicle operation.

FIG. 5 illustrates an alternate battery pack thermal management system500 also applicable to the battery pack cooling system of the presentinvention. In system 500 the coolant within conduits 401 is coupled to asecondary thermal management system 501 via a heat exchanger 503.Preferably thermal management system 501 is a refrigeration system andas such, includes a compressor 505 to compress the low temperature vaporin refrigerant line 507 into a high temperature vapor and a condenser509 in which a portion of the captured heat is dissipated. After passingthrough condenser 509, the refrigerant changes phases from vapor toliquid, the liquid remaining at a temperature below the saturationtemperature at the prevailing pressure. The refrigerant then passesthrough a dryer 511 that removes moisture from the condensedrefrigerant. After dryer 511, refrigerant line 507 is coupled to heatexchanger 503 via thermal expansion valve 513 which controls the flowrate of refrigerant into heat exchanger 503. Additionally, in theillustrated system a blower fan 515 is used in conjunction withcondenser 509 to improve system efficiency.

In a typical vehicle configuration, thermal management system 501 isalso coupled to the vehicle's heating, ventilation and air conditioning(HVAC) system. In such a system, in addition to coupling refrigerantline 507 to heat exchanger 503, line 507 may also be coupled to the HVACevaporator 517. A thermal expansion valve 519 is preferably used tocontrol refrigerant flow rate into the evaporator. A heater, for examplea PCT heater 521 integrated into evaporator 517, may be used to providewarm air to the passenger cabin. In a conventional HVAC system, one ormore fans 523 are used to circulate air throughout the passenger cabin,where the circulating air may be ambient air, air cooled via evaporator517, or air heated by heater 521.

In some electric vehicles, battery pack cooling is accomplished using acombination of a radiator such as that shown in FIG. 4, and a heatexchanger such as that shown in FIG. 5. FIG. 6 illustrates such acooling system. In system 600, the coolant passing through battery pack101 via conduits 401 may be directed through either radiator 601 or heatexchanger 503. Valve 603 controls the flow of coolant through radiator601. Preferably a blower fan 605 is included in system 600 as shown,thus providing means for forcing air through the radiator whennecessary, for example when the car is stationary. Note that it shouldbe understood that the cooling conduit configuration for battery pack101 shown in FIGS. 4-6 is only for illustration purposes and that thesethermal management systems are equally applicable to otherconfigurations. For example, FIG. 7 shows the cooling system of FIG. 4with a different conduit configuration within battery pack 101, oneutilizing coolant manifolds.

While conventional battery pack cooling conduits such as those shown inFIGS. 2 and 3 provide a means for maintaining battery temperature withina desired range, due to their integration within the confines of thebattery pack they present a number of risks and limitations. First, dueto their inclusion within the battery pack, battery pack complexity issignificantly increased, affecting both manufacturing time and cost.Second, due to pack complexity, if a leak occurs within the integratedcoolant conduits repair may be exceedingly difficult and costly,potentially requiring pack or module replacement. Third, if the coolantis electrically conductive, even a minor leak can lead to catastrophicdamage due to the leaking coolant creating a battery short. As notedabove, a battery short can lead to a thermal runaway event, potentiallydestroying not only the battery pack but also the entire vehicle,property near the vehicle (e.g., garage and/or house), and risking thehealth and welfare of the vehicle's passengers. Fourth, a leak of evennon-electrically conductive coolant within the battery pack can damagesensitive interconnects and other pack components, resulting in costlyrepairs and in some instances requiring the complete replacement of thedamaged pack or module.

In order to overcome the limitations inherent in a battery pack thermalmanagement system in which the cooling conduits are integrated into thebattery pack, the present inventors utilize cooling conduits that areexternal to the pack. FIG. 8 provides a cross-sectional view of anexemplary battery pack 800 configured in accordance with a preferredembodiment of the invention. Battery pack 800, which does notincorporate cooling conduits within the pack, includes a lower enclosurepanel 801, side panels 803 and an upper enclosure panel 805. Containedwithin pack 800 is a plurality of batteries 807, preferably cylindricalbatteries utilizing an 18650 form factor. Batteries 807 are positionedwithin the battery pack such that the cylindrical axis of each cell issubstantially perpendicular to the upper and lower battery packenclosure panels and where the cap assembly of each of the batteries isadjacent to lower enclosure panel 801. It should be understood that FIG.8 is simply intended to illustrate the invention, and that a batterypack in accordance with the invention may include more or less batteriesthan shown.

Rechargeable batteries often incorporate a variety of protectionmechanisms into the battery's cap assembly, mechanisms such as apositive temperature coefficient current limiter and a current interruptdevice. In addition, the cap assembly typically includes a ventingmechanism that is designed to rupture at high pressures, therebyproviding a pathway for gas and other materials to escape the confinesof the battery casing. In general, the venting mechanism directs theflow of gas and material during a thermal runaway event out through thecap assembly and in a direction that is substantially parallel to thebatteries cylindrical axis. Accordingly, during a thermal runaway eventbatteries 807 will generally direct the flow of hot gas and othermaterials downward in a direction 809 towards the road surface 207, andthus away from the passenger cabin which is situated above the batterypack.

In the battery pack of the invention, the bus bars are all located atone end of the batteries, thereby simplifying pack fabrication andallowing heat removal from the other end of each of the batteries. FIG.9 provides a simplified view of such an interconnect configuration. Asshown, the positive battery terminals (e.g., nub 901 projecting from thecap assembly) and the negative battery terminals (e.g., the batterycasing 903) are coupled to bus bars 905-908 using battery interconnects909 (e.g., wire bonds). In particular, bus bars 905 and 908 couple thefirst group of batteries 807A and 807B in parallel, bus bars 908 and 906couple the second group of batteries 807C and 807D in parallel, and busbars 906 and 907 couple the third group of batteries 807E and 807F inparallel. Series connections between battery groups are formed by thebus bars, specifically the second bus bar 908 connects the positiveterminals of the first group of batteries 807A and 807B to the negativeterminals of the second group of batteries 807C and 807D, and the thirdbus bar 906 connects the positive terminals of the second group ofbatteries 807C and 807D to the negative terminals of the third group ofbatteries 807E and 807F. In the illustrated bus bar stackingarrangement, first bus bar 905 and third bus bar 906, which areseparated by an air gap or other electrical insulator to prevent shortcircuiting, are placed in a first layer 911; similarly, second bus bar908 and fourth bus bar 907, which are also separated by a gap orinsulator, are placed in a third layer 913. Disposed between layers 911and 913 is an electrically insulating layer 915.

As noted above, the present invention relies on a battery interconnectconfiguration in which all battery/bus bar connections are made at oneend of the batteries, preferably the lower end of the batteries, thusfreeing up the upper end of each of the batteries for heat removal. Itshould be understood that the invention is not limited to a particularbus bar configuration. For example, the invention may use a multi-layerbus bar configuration such as that described and illustrated inco-assigned U.S. patent application Ser. No. 14/203,874, filed 11 Mar.2014, the disclosure of which is incorporated herein for any and allpurposes. Alternately, the invention may use a non-stacking bus bararrangement such as the configuration described and illustrated inco-assigned U.S. patent application Ser. No. 14/802,207, filed 17 Jul.2015, the disclosure of which is incorporated herein for any and allpurposes. To simplify the figures illustrating the invention, thebattery interconnects and the battery mounts are not shown.

In accordance with the invention, battery casing surface 811 of eachbattery 807 is thermally coupled to the flat battery pack enclosurepanel (e.g., panel 805) with a layer 813 of a thermally conductive,electrically non-conductive material. Surface 811, which is comprised ofa portion of the battery case (i.e., casing) is the uppermost surface ofthe battery and is opposite the end of the battery containing the capassembly. Layer 813, which provides thermal communication between eachof the batteries and pack enclosure panel 805, may be formed as adiscontinuous layer such that each battery is thermally coupled to panel805 by its own portion or region of layer 813 as shown. Alternately,this thermally conductive, electrically non-conductive layer may beformed as a continuous layer 1001 as shown in FIG. 10. Furthermore, thislayer may only contact the uppermost surface 811 of the battery asexemplified in pack 800 of FIG. 8, or this layer may contact theuppermost surface 811 as well as upper battery portion 1003 asexemplified in pack 1000 of FIG. 10.

Layer 813 (and layer 1001) may be formed of any material that providesadequate thermal conductivity while providing the necessary levels ofelectrical isolation to prevent battery shorting. In at least oneembodiment this layer is comprised of an epoxy. Preferably layer 813(and layer 1001) has a resistivity of at least 10¹² ohm-cm and a thermalconductivity of at least 0.25 Wm⁻¹K⁻¹, and more preferably a thermalconductivity of at least 0.50 Wm⁻¹K⁻¹, and still more preferably athermal conductivity of at least 0.75 Wm⁻¹K⁻¹. Although not required, inat least one embodiment of the invention, and as described in detail inco-pending and co-assigned U.S. patent application Ser. No. 14/331,300,filed 15 Jul. 2014, the disclosure of which is incorporated herein forany and all purposes, a plurality of electrically non-conductivegranules, for example fabricated from alumina or silica, are dispersedwithin layer 813 (and/or layer 1001), where the granules have a highermelting point than the material comprising layer 813 (and layer 1001).As a result of the granules, even if the thermally conductive layersoftens due to excessive heat, the granules help prevent the batteriesfrom contacting enclosure panel 805, thereby preventing shorting ifpanel 805 is fabricated from an electrically conductive material (e.g.,metal).

Panel 805 is fabricated from a thermally conductive material. Preferablypanel 805 is fabricated from a metal such as aluminum with a thermalconductivity on the order of 100-200 Wm⁻¹K⁻¹, or an iron alloy such as acarbon steel with a thermal conductivity on the order of 40-60 Wm⁻¹K⁻¹or stainless steel with a thermal conductivity on the order of 15-20Wm⁻¹K⁻¹. Panel 805, more specifically the inner surface relative to thebattery pack, may include a thin layer of an electrically non-conductivematerial, i.e., an isolation layer, thereby providing further protectionfrom battery shorting in the event of excessive heating causing layer813 (or layer 1001) to soften and fail. If panel 805 is fabricated fromaluminum, in at least one embodiment it is anodized in order to createan electrically non-conductive layer.

Attached to the outer surface of enclosure panel 805, i.e., surface 815,is a conduit panel 817 that serves as the outer surface of the coolingconduit structure. Panel 817 may be fabricated using a stamping processor any other technique that is capable of generating the desired patternin the selected material (e.g., aluminum, iron alloy such as carbonsteel or stainless steel, etc.). The portion of conduit panel 817 shownin the cross-sectional view of FIG. 8 is comprised of a corrugatedstructure. The corrugated structure provides both mounting surfaces 819and coolant channels 821, where mounting surfaces 819 may be welded,brazed, soldered, or bonded to surface 815 of panel 805. In FIG. 8,joint 823 is indicative of this attachment juncture (i.e., a weld joint,braze joint, solder joint or bonding joint). FIG. 11 is a top view of aconduit panel 1100, similar to panel 817 except for the number ofconduits channels 1101. A thermal transfer medium, also referred toherein as a coolant, is pumped through the channels formed by theconduit panel and the underlying enclosure panel (e.g., panel 805) withthe coolant entering through conduit input 1103 and exiting via conduitoutput 1105. It should be understood that the conduit panel of theinvention is not limited to a specific channel shape or channelconfiguration. For example, FIG. 12 illustrates an alternatecross-sectional channel shape in a conduit panel 1201 that includes adifferent pitch (i.e., channel spacing 1203).

A coolant conduit structure in accordance with the invention and asdescribed above offers a number of significant advantages over aconventional battery cooling system such as those shown in FIGS. 2 and3. Firstly, if the conduit structure leaks, the leaking coolant cannotenter the battery pack and therefore cannot short or otherwise damagethe batteries and internal battery pack components (e.g., interconnects,fuse assembly, etc.). Therefore the risk of damaging the battery pack,one of the most expensive components in an EV, is significantly reduced.Secondly, many types of conduit leaks, such as those occurring at ajuncture between the conduit panel (e.g., panel 817, panel 1100, panel1201, etc.) and the underlying panel (e.g., pack enclosure panel 805),will be of minor consequence if they only cause a small amount ofcoolant to bypass a portion of the cooling system. For example and asillustrated in FIG. 13, a leak occurring at junction 823A will simplycause fluid to flow between coolant channels 821A and 821B, therebycausing minimal degradation in thermal control efficiency. Furthermore,a leak such as that described above and illustrated in FIG. 13 willtypically not even require immediate repair. In contrast, a similarlysized leak occurring within an internally mounted cooling conduit (e.g.,conduit 209 in FIG. 2 or conduit 301 in FIG. 3) would require immediateand costly repair. Thirdly, when a cooling conduit does require repair,for example due to a leak on an external surface of the conduit panel,the repair can be performed without requiring the complete disassemblyof the battery pack. Rather, the conduit repair can be accomplished bysimply replacing the battery enclosure panel 805 and the attachedconduit panel (e.g., panel 817). Fourthly, since the cooling conduitsare externally mounted, the battery pack complexity is dramaticallyreduced, thereby reducing manufacturing time and cost.

As noted above, panel 805 is preferably fabricated from a metal such asaluminum or steel (e.g., carbon steel, stainless steel, etc.). Aluminumprovides superior thermal conductivity, thus efficiently conducting theheat from the batteries to the coolant within the channels (e.g.,channels 821) of the conduit panel as well as effectively spreading theheat between batteries and helping to prevent hot spots. Steel, due toits higher melting point, provides a more effective barrier between thebattery pack and the passenger cabin in the event of a batteryundergoing thermal runaway. Accordingly, in at least one preferredembodiment either the upper enclosure panel (e.g., panel 805) or theconduit panel (e.g., panel 817, panel 1201) or both is fabricated fromsteel.

In a modification of the embodiment described above, and as illustratedin FIG. 14, a three layer design may also be used for the thermalmanagement system. This embodiment is similar to that described above,except for the inclusion of a secondary panel interposed between thebattery pack enclosure panel and the conduit panel. The use of a threelayer design allows the cooling panel structure, as a whole, to beremoved without opening the battery pack. Therefore as a result of thisdesign configuration, the initial vehicle fabrication costs may bereduced as well as those costs associated with vehicle maintenance,thereby reducing the cost of ownership.

As shown in FIG. 14, interposed between upper battery pack enclosurepanel 805 and conduit panel 817 is a secondary flat panel 1401. Theconduit panel, which may utilize any coolant channel cross-section orconfiguration as noted above, is attached via mounting surfaces 819 tosecondary panel 1401 via a weld joint, braze joint, solder or bondingmaterial 823. While panel 1401 may be welded, brazed, soldered or bondedto the upper battery pack enclosure panel (e.g., panel 805), preferablyit is attached via a technique such as clips or bolts (e.g., bolts 1403)that allow the easy removal and replacement of the conduit structurefrom the battery pack. In at least one embodiment, a thermal compound(e.g., grease, paste or gel) is interposed between panel 1401 and upperbattery pack enclosure panel 805, thereby improving heat transferbetween the battery pack and the cooling conduits.

In order to achieve the desired level of performance andmanufacturability, several constraints are placed on the upper batterypack enclosure panel, the secondary panel, and the conduit panel. Forexample, the materials comprising the upper battery pack enclosure panel(e.g., panel 805) and the interposed panel (e.g., panel 1401) must bethermally conductive in order to insure adequate transfer of heat fromthe batteries to the coolant within the channels of the conduit panel.Furthermore, one or more of the three panels is preferably fabricatedfrom steel, thereby providing a fire protection layer that insuresadequate passenger protection from any thermal runaway events that occurwithin the battery pack. Additionally, the conduit panel (e.g., panel817) must be fabricated from a material that can be attached to theinterposed panel (e.g., panel 1401) by the desired attachment means(e.g., welding, brazing, etc.). In light of these requirements, in onepreferred configuration the upper battery pack enclosure panel isfabricated from aluminum while both the conduit panel and the interposedpanel are fabricated from an iron alloy (e.g., carbon steel, stainlesssteel, etc.). In an alternate configuration, the upper battery packenclosure panel is fabricated from an iron alloy (e.g., carbon steel,stainless steel, etc.) while both the conduit panel and the interposedpanel are fabricated from aluminum. In yet another configuration, theupper battery pack enclosure panel and the conduit panel are fabricatedfrom an iron alloy while the interposed panel is fabricated fromaluminum. In yet another configuration, the upper battery pack enclosurepanel and the conduit panel are fabricated from aluminum while theinterposed panel is fabricated from an iron alloy. The last twoconfigurations help to offset the bimetallic effect, although theyrequire that the conduit panel be attached to a panel of a dissimilarmaterial.

In order to provide further optimization, the inventors have found thatin some instances a four layer design is preferable. As in the priorembodiments, each of the layers interposed between the batteries and thecoolant is fabricated from a thermally conductive material, preferably ametal such as aluminum or an iron alloy. Given the need for a thermallyconductive material, and given that weight is a principal concern in anEV where increased weight translates to reduced performance and range,aluminum is an ideal candidate for the structure. However, and aspreviously noted, due to its higher melting point steel provides a moreeffective fire barrier than aluminum in the event of a batteryundergoing thermal runaway. Accordingly in at least one preferredembodiment, at least one of the layers is comprised of an iron alloysuch as carbon steel or stainless steel. An additional concern,regardless of the embodiment, is the coolant channel seal between theconduit panel and the adjacent panel. In addition to being a highquality seal, preferably it is fabricated using a rapid and inexpensivetechnique such as laser welding. The inventors have found that thesegoals are best achieved when using similar materials for the conduitpanel and the immediately adjacent panel (e.g., an aluminum-aluminuminterface or a steel-steel interface).

To achieve the above design goals, in a preferred four layer design thatoptimizes thermal performance and weight, both conduit panel 817 andadjacent panel 1501 are fabricated from aluminum. In addition, in thisdesign enclosure panel 805 and secondary panel 1501 are fabricated fromthe same material, i.e., aluminum. A tertiary panel 1503, interposedbetween enclosure panel 805 and secondary panel 1501, is fabricated froman iron alloy (e.g., carbon steel or stainless steel). Thus this designallows easy removal and/or replacement of the conduit structure, the useof simple fabrication techniques (e.g., welding) for the conduitstructure, and the inclusion of a fire protection layer, all in arelatively low weight structure. It should be understood, however, thatthe four layer design of the invention may utilize other materialcombinations. For example, in an alternate configuration upper enclosurepanel 805, conduit panel 817 and secondary panel 1501 are all fabricatedfrom steel while tertiary panel 1503 is fabricated from aluminum.

Regardless of the materials selected for each of the panels in the fourlayer design, preferably a thermal compound (e.g., thermal grease, pasteor gel) is interposed between panels 805 and 1503, and interposedbetween panels 1503 and 1501, thereby improving heat transfer.

Systems and methods have been described in general terms as an aid tounderstanding details of the invention. In some instances, well-knownstructures, materials, and/or operations have not been specificallyshown or described in detail to avoid obscuring aspects of theinvention. In other instances, specific details have been given in orderto provide a thorough understanding of the invention. One skilled in therelevant art will recognize that the invention may be embodied in otherspecific forms, for example to adapt to a particular system or apparatusor situation or material or component, without departing from the spiritor essential characteristics thereof. Therefore the disclosures anddescriptions herein are intended to be illustrative, but not limiting,of the scope of the invention.

What is claimed is:
 1. A battery pack thermal management assembly,comprising: a plurality of batteries, each battery of said plurality ofbatteries comprising a first terminal at a first end portion of saidbattery and a second terminal at said first end portion of said battery;a sealed battery pack enclosure configured to contain said plurality ofbatteries, said sealed battery pack enclosure comprising a lowerenclosure panel, a plurality of enclosure side panels, and an upperenclosure panel, and wherein said upper enclosure panel is comprised ofa thermally conductive material; a conduit panel, wherein at least aportion of said conduit panel in cross-section exhibits a corrugatedstructure, said corrugated structure comprising a plurality of mountingsurfaces and a plurality of channels; a secondary panel, wherein a firstsurface of said secondary panel is attached to said conduit panel at aplurality of attachment junctures, wherein at least a portion of saidplurality of attachment junctures are formed between said first surfaceof said secondary panel and said plurality of mounting surfaces, whereinsaid plurality of attachment junctures form a coolant channel seal,wherein said conduit panel and said secondary panel comprise a coolingpanel structure, said cooling panel structure further comprising acoolant channel, said coolant channel defined by said first surface ofsaid secondary panel and an inner surface of said plurality of channelsof said corrugated structure of said conduit panel; a tertiary panelinterposed between an external surface of said upper enclosure panel anda second surface of said secondary panel, wherein said tertiary panel isthermally coupled to said upper enclosure panel and said secondarypanel; and a layer of thermally conductive material, wherein said layerof thermally conductive material is electrically insulative, whereinsaid layer of thermally conductive material contacts and is thermallycoupled to at least an upper surface of each battery of said pluralityof batteries, wherein said upper surface of each battery is distal fromsaid first end portion of each battery, and wherein said layer ofthermally conductive material is interposed between said upper surfaceof each battery of said plurality of batteries and an internal surfaceof said upper enclosure panel.
 2. The battery pack thermal managementassembly of claim 1, wherein said cooling panel structure is attached tosaid tertiary panel via a temporary means of attachment selected fromthe group consisting of bolts and clips.
 3. The battery pack thermalmanagement assembly of claim 1, wherein said cooling panel structure isattached to said tertiary panel using a technique selected from welding,brazing, soldering and bonding.
 4. The battery pack thermal managementassembly of claim 1, wherein said tertiary panel is attached to saidupper enclosure panel via a temporary means of attachment selected fromthe group consisting of bolts and clips.
 5. The battery pack thermalmanagement assembly of claim 1, wherein said tertiary panel is attachedto said upper enclosure panel using a technique selected from welding,brazing, soldering and bonding.
 6. The battery pack thermal managementassembly of claim 1, further comprising a layer of a thermal compoundinterposed between a first surface of said tertiary panel and saidsecond surface of said secondary panel, wherein said thermal compound isselected from the group consisting of thermal greases, thermal pastesand thermal gels.
 7. The battery pack thermal management assembly ofclaim 1, further comprising a layer of a thermal compound interposedbetween said external surface of said upper enclosure panel and saidtertiary panel, wherein said thermal compound is selected from the groupconsisting of thermal greases, thermal pastes and thermal gels.
 8. Thebattery pack thermal management assembly of claim 1, wherein said sealedbattery pack enclosure is mounted to a vehicle, wherein said first endportion of each battery of said plurality of batteries is in closeproximity to said lower enclosure panel, wherein said lower enclosurepanel is adjacent to a road surface, and wherein said upper surface ofeach battery of said plurality of batteries is in close proximity tosaid internal surface of said upper enclosure panel.
 9. The battery packthermal management assembly of claim 8, wherein each battery of saidplurality of batteries utilizes a cylindrical form factor, and whereinsaid plurality of batteries are positioned within said sealed batterypack enclosure such that a cylindrical axis corresponding to eachbattery of said plurality of batteries is substantially perpendicular tosaid lower enclosure panel.
 10. The battery pack thermal managementassembly of claim 9, wherein said coolant channel is positioned suchthat a coolant within said coolant channel flows within a plane that issubstantially perpendicular to said cylindrical axis corresponding toeach of said plurality of batteries.
 11. The battery pack thermalmanagement assembly of claim 1, wherein said plurality of attachmentjunctures are fabricated using a technique selected from welding,brazing, soldering and bonding.
 12. The battery pack thermal managementassembly of claim 1, wherein said plurality of attachment junctures arecomprised of at least one of a weld joint, a braze joint, a solder jointand a bonding joint.
 13. The battery pack thermal management assembly ofclaim 1, wherein said external surface of said upper enclosure panel isflat, wherein said first and second surfaces of said secondary panel areflat, and wherein said tertiary panel is flat.
 14. The battery packthermal management assembly of claim 1, further comprising: a heattransfer medium contained within said coolant channel; and a circulationpump configured to pump said heat transfer medium through said coolantchannel.
 15. The battery pack thermal management assembly of claim 1,wherein said layer of thermally conductive material is discontinuous andcomprised of a plurality of thermally conductive material regions,wherein said plurality of thermally conductive material regionscorrespond to said plurality of batteries.
 16. The battery pack thermalmanagement assembly of claim 1, wherein said layer of thermallyconductive material contacts and is thermally coupled to a second endportion of each battery of said plurality of batteries, wherein saidsecond end portion of each battery is distal from said first end portionof each battery.
 17. The battery pack thermal management assembly ofclaim 1, further comprising a plurality of granules dispersed throughoutsaid layer of thermally conductive material, wherein a first meltingpoint corresponding to said plurality of granules is higher than asecond inciting point corresponding to said layer of thermallyconductive material.
 18. The battery pack thermal management assembly ofclaim 1, wherein said upper enclosure panel is fabricated from a metalselected from the group consisting of aluminum and iron alloys.
 19. Thebattery pack thermal management assembly of claim 1, wherein said upperenclosure panel has a thermal conductivity of at least 15 Wm⁻¹K⁻¹. 20.The battery pack thermal management assembly of claim 19, wherein saidupper enclosure panel has a thermal conductivity of at least 40 Wm⁻¹K⁻¹.21. The battery pack thermal management assembly of claim 20, whereinsaid upper enclosure panel has a thermal conductivity of at least 100Wm⁻¹K⁻¹.
 22. The battery pack thermal management assembly of claim 1,wherein said secondary panel is fabricated from a metal selected fromthe group consisting of aluminum and iron alloys.
 23. The battery packthermal management assembly of claim 1, wherein said secondary panel hasa thermal conductivity of at least 15 Wm⁻¹K⁻¹.
 24. The battery packthermal management assembly of claim 23, wherein said secondary panelhas a thermal conductivity of at least 40 Wm⁻¹ ⁻¹.
 25. The battery packthermal management assembly of claim 24, wherein said secondary panelhas a thermal conductivity of at least 100 Wm⁻¹K⁻¹.
 26. The battery packthermal management assembly of claim 1, wherein said tertiary panel isfabricated from a metal selected from the group consisting of aluminumand iron alloys.
 27. The battery pack thermal management assembly ofclaim 1, wherein said tertiary panel has a thermal conductivity of atleast 15 Wm⁻¹K⁻¹.
 28. The battery pack thermal management assembly ofclaim 27, wherein said tertiary panel has a thermal conductivity of atleast 40 Wm⁻¹K⁻¹.
 29. The battery pack thermal management assembly ofclaim 28, wherein said tertiary panel has a thermal conductivity of atleast 100 Wm⁻¹K⁻¹.
 30. The battery pack thermal management assembly ofclaim 1, wherein said conduit panel is fabricated from a metal selectedfrom the group consisting of aluminum and iron alloys.
 31. The batterypack thermal management assembly of claim 1, wherein said layer ofthermally conductive material has a resistivity of at least 10¹² ohm-cmand a thermal conductivity of at least 0.25 Wm⁻¹K⁻¹.
 32. The batterypack thermal management assembly of claim 31, wherein said thermalconductivity of said layer of thermally conductive material is greaterthan 0.75 Wm⁻¹K−¹.
 33. The battery pack thermal management assembly ofclaim 1, wherein said layer of thermally conductive material iscomprised of an epoxy.
 34. The battery pack thermal management assemblyof claim 1, wherein said inner surface of said upper enclosure panel iscoated with an isolation layer comprised of an electricallynon-conductive material.
 35. The battery pack thermal managementassembly of claim 1, wherein said upper enclosure panel is fabricatedfrom aluminum, and wherein said inner surface of said upper enclosurepanel is anodized.